I have a query

My partner is a social worker  and works for a local authority. Her manager has started a disciplinary on the ground that she has received complaints from some customers that she has been rude and condescending.

She has been a social worker for past 11 years and had an unblemished service. However, since February there has been a change in management a new manager has started managing her. The manager has been a bully and has been harassing for some time and whenever she had undergone supervision she has come out crying. In this she had been taking advice from Unions and they had suggested that they put in a grievance against the manager. But she did not want to get involved in any controversy.

First time, in February 2014 someone had complained but the complained was never disclosed nor discussed and she was asked not contact the customer. In subsequent months the same process was followed i.e.  such and such customer has complained and they don't want you contact them. However, she was not given any information about the content of the complaint and was never asked to give an explanation or was never asked her version.

In the beginning of August, she was called in and then was the first time the complaints were discussed and in that meeting too the manager was aggressive and used comments like "Who are you to question the customers", "how dare you say this", "who do you think you are" etc. 

After two weeks she was again called in was told that a disciplinary has been initiated against her. 

In addition, I would also like to mention that she has received compliments from other customers and glowing reference from previous manager. As there are no witnesses and it will be her word against the customers, how can she defend her self?